The present invention relates generally to the stretching of sheet materials and more particularly to an apparatus and method for stretching extensible sheet materials such as nonwoven webs and laminates.
Sheet materials such as nonwoven webs, fabrics, films, and laminates are used in a wide variety of applications such as garments, disposable medical products, diapers and personal hygiene products. New products being developed for these applications have demanding performance requirements, including comfort, conformability to the body, freedom of body movement, good softness and drape, adequate tensile strength and durability and resistance to surface abrasion.
In many instances, it may be desirable to stretch the sheet material to provide improved properties such as softness, elasticity, drape, and the like. According to Sabee, U.S. Pat. Nos. 4,153,664 and 4,223,063, the softness and drapeability of nonwoven fabrics can be improved by drawing or stretching the fabric. More particularly, according to these patents the nonwoven fabrics are processed by differentially drawing or stretching the web by passing the fabric through a pair of intermeshing grooved rolls to form a pattern of drawn and undrawn areas.
For some applications, the nonwoven fabric must have elastic properties. In certain disposable diaper designs, for example, it is desired to impart elasticity to the waist and/or to the leg cuff areas. One approach to imparting elastic properties to a nonwoven fabric is with a so-called “zero-strain” stretchable laminate. A “zero-strain” stretchable laminate refers to a fabric in which at least two layers of material, one elastic and the other substantially inelastic, are secured to one another along their coextensive surfaces while in a substantially untensioned state. The fabric is subsequently subjected to mechanical stretching by “ring-rolling”—a process wherein the laminate is directed between one or more pairs of intermeshed grooved rolls. This causes the inelastic layer to be permanently elongated and gives the laminate elastic properties. Conventional ring-rolling process for mechanically stretching the sheet material are limited to stretching the sheet in the machine direction and/or in the cross-machine section direction of the sheet material. As a result, the stretched material has elastic properties along either the machine direction or the cross direction or both. However, for many materials, it would be desirable to have a material having elastic properties in more than two directions. For example, in clothing applications, to permit free movement in all directions it may be desirable to provide a material that is stretched in multiple directions and has elastic properties along multiple directions.